The present invention relates to an apparatus for using a Leroux-Gueguen algorithm for coding a signal by linear prediction.
The invention applies to the processing of widely varying signals (seismic, biological, speech, radar, telephone and similar signals).
For example, in the case of a low rate television signal transmission, it is desirable to represent the speech signal in a very condensed form, but which still makes it possible to maintain a good intelligibility of speech when the condensed signal is received. Therefore the aim is to produce a synthetic signal which resembles as closely as possible the original signal by a modeling procedure, called coding by linear prediction. This coding involves the signal being sampled at a constant frequency. On the basis of the samples taken for a period for which it is assumed that the statistical characteristics of the signal remain constant, a calculation takes place of the correlation coefficients R.sub.i of the sampled signal, i being an integer ranging e.g. between 0 and 10. These coefficients make it possible to obtain a significant condensing of the characteristic informations of the signal. These correlation coefficients give a good representation model of the original signal. The correlation coefficients R.sub.i, as well as the obtaining thereof are described in the article "Single Chip LPC Vocoder" by Stephen P. Pope et al published in IEEE International Solid State Circuits Conference, pp. 118-119, Feb. 22, 1984.
It is also known that after calculating these correlation coefficients, it is then necessary to carry out a non-linear transformation thereof to other coefficients K.sub.i, which are called "partial correlation coefficients", which have better sensitivity, classification, coding and similar properties. These coefficients are also called PARCOR coefficients.
The non-linear transformation making it possible to obtain the partial correlation coefficients K.sub.i from correlation coefficients R.sub.i is carried out by using the LEROUX-GUEGUEN algorithm, which is described in an article entitled "A Fixed Point Computation of Partial Correlation Coefficients" by J. Leroux and C. Gueguen published in IEEE Transactions on ASSP in June 1977.
The known apparatuses making it possible to use the LEROUX-GUEGUEN algorithm for obtaining partial correlation coefficients from the correlation coefficients of a signal generally make use of processors associated with memories, together with adders, multiplyers, etc. These apparatuses have a complicated architecture. They require processing programs for obtaining partial correlation coefficients. In no case can these apparatuses constitute a single integrated circuit of small size. They generally occupy a large surface area and their components can cover several cards.
The invention aims at obviating the disadvantages of the existing apparatuses, making it possible to utilize the LEROUX-GUEGUEN algorithm for coding a signal by linear prediction. The invention more particularly makes it possible to obtain an apparatus which can be in the form of a single integrated circuit (or part of a circuit), which has a small surface area, is inexpensive and requires no processing program. Throughout the remainder of the description the partial correlation coefficients will be referred to as PARCOR coefficients.